gms | German Medical Science

Objectives: Glenoid bone loss is one of the most important risk factors for recurrent anterior shoulder instability. Bony reconstruction is recommended in critical bone loss (>15%). Commonly used surgical techniques including coracoid transfer were associated with considerable complications. Scapular-spine-blocks have been defined as a potential alternative. The purpose of this study was to assess the micromotion at the glenoid-bone-block interface after coracoid and spina-scapula bone-block reconstruction of the anterior glenoid.

Methods: A total of 12 ethanol-glycerin fixed cadaveric shoulder specimen were tested in this study. A 20% bone defect of the anterior glenoid was created to simulate critical bone loss. Specimen were randomly assigned to surgical glenoid augmentation using a coracoid bone-block (n=6) or surgical glenoid augmentation using a scapular spine bone-block (n=6). The glenoid-bone interface was cyclically loaded using a modified ‘rocking horse’ setup as defined by the ASTM F2028. A force of 170 N was applied and a complete test consisted of 5,000 cycles. The micromotion at the bone-bone interface was tracked using an optical 3D measurement system (GOM ARMIS) and was evaluated with the digital image correlation software GOM Correlate Pro.

Results and conclusion: The most dominant micromotion component was medial/lateral irreversible displacement with a mean displacement of 1.87 mm (SD 1.11 mm) for the spina-scapula block and 0.91 mm (SD 0.29 mm) for the coracoid block (p=0.07). The greatest medial/lateral irreversible displacement took place during the first nine cycles, with a mean medial/lateral irreversible displacement of 1.05 mm (SD 0.50 mm) for spina-scapula blocks and 0.58 mm (SD 0.31 mm) for coracoid bone blocks. Inferior reversible displacement was significantly greater for spina-scapula blocks (-0.28 mm, SD 0.16 mm) compared to coracoid bone blocks (-0.06 mm, SD 0.10 mm) (p=0.02).

After reconstruction of critical bone loss of the anterior glenoid medial irreversible displacement is the dominant micromotion component. Except for inferior reversible displacement there are no significant differences in irreversible and reversible displacement between coracoid and spina-scapula bone blocks. In our study coracoid and spina-scapula bone blocks therefore seem to have comparable biomechanical primary stability. Further studies are needed to verify the results.